AB0087 THE EFFECT OF BARICITINIB ON STAT1 PHOSPHORYLATION IN MONOCYTES FROM RHEUMATOID ARTHRITIS PATIENTS
Authors: C. Garufi, G. Tucci, I. Pacella, M. Zagaglioni, A. Pinzon Grimaldos, F. Ceccarelli, S. Piconese, F. R. Spinelli, F. Conti
Journal: Annals of the Rheumatic Diseases (2022)

Background Baricitinib is a Janus kinase (JAK)1/JAK2 inhibitor approved for the treatment of rheumatoid arthritis (RA) 1-2 . STAT proteins bind JAK kinase dimers coupled with cytokine receptors and regulate gene transcription. The JAK/STAT system is responsible for the intracellular signaling of different cytokines contributing to the activation process of the monocyte lineage, therefore the use of JAK inhibitors can affect cell functionality 3-6 . Objectives The aim of the present study was to verify the effects of baricitinib on STAT phosphorylation in peripheral mononuclear cells (PBMCs) of RA patients and to evaluate any correlation between STAT phosphorylation and response to therapy. Methods At baseline (BL) and after 4 weeks (w4) of treatment, we evaluated patients’ disease activity (DAS28 PCR , CDAI and SDAI), dividing them into responders and non-responders according to the Minimal Clinically Important Difference for DAS28 PCR (1.2 points) at w4. The phosphorylation of STAT1, STAT4 and STAT5 was analyzed at BL and w4 in gated monocytes, Treg, CD8 + and CD4 + lymphocytes from 4 responder and 4 non-responder patients through flow cytometry, at basal conditions and after IL2, IFNα and IL6 stimulation. Results Baseline clinical and demographic characteristics of patients are reported in Table 1. We showed that monocyte count decreased from BL to w4 mostly in responders. Basal pSTAT1 phosphorylation tent to be higher in monocytes of non-responder patients; after 4 weeks of treatment, the reduction of the cytokine-induced pSTAT1 was significantly greater in monocytes from responders compared to non-responders (Figure 1). The phosphorylation of STAT4 and STAT5 was not affected by treatment in any cell type and at any time point. We further studied the STAT1 phosphorylation pathway isolating the effect of stimulation with IFNα and stratifying monocytes according to their surface marker expression of CD14 and CD16 in classical, intermediate and non-classical. We observed the same pattern with a significant greater reduction of pSTAT1 in monocytes from responder patients, compared to non-responders, after the treatment with baricitinib. Table 1. Clinical and demographic characteristics of Rheumatoid Arthritis patients. Clinical and demographic characteristics N=8 Age (years), median (IQR) 59 (8) Female:Male 7:1 Etnicity -Caucasian n (%) 6 (75) -Hispanic n (%) 2 (25) Disease duration (months), median (IQR) 156 (201) Rheumatoid Factor, n (%) 3 (37.5) ACPA, n (%) 4 (50) Number of previous csDMARDs, n (%) -1 2 (25) -2 1 (12.5) -3 1 (12.5) -≥ 4 4 (50) Number of previous bDMARDs, n (%) -1 2 (25) -2 2 (25) -3 1 (12.5) -≥ 4 3 (37.5) Baricitinib in monoterapy, n (%) 5 (62.5) Daily PDN dose, median (IQR) 5 (6) ACPA: anti-citrullinated protein antibodies; csDMARDs: conventional syntetic disease-modifying antirheumatic drugs; bDMARDs: biological disease-modifying antirheumatic drugs; PDN: prednisone. Figure 1. STAT1 phosphorylation in responder (R) and non-responder (NR) patients at basal conditions (before stimulation) (a), and after cytokine (IL2, IFNα and IL6) stimulation (b) at baseline and at T1 (week 4). Conclusion These results may suggest that monocyte count and STAT1 phosphorylation in circulating monocytes could represent early markers of response to baricitinib therapy. References [1]Gadina M, et al. Janus kinases to jakinibs: from basic insights to clinical practice. Rheumatology (Oxford). 2019 [2]Gadina M, et al. Translating JAKs to Jakinibs. J Immunol. 2020 [3]Kubo S, et al. The JAK inhibitor, tofacitinib, reduces the T cell stimulatory capacity of human monocyte-derived dendritic cells. Ann Rheum Dis. 2014 [4]Kubo S, et al. Janus Kinase Inhibitor Baricitinib Modulates Human Innate and Adaptive Immune System. Front Immunol. 2018 [5]Ikari Y, et al. Peficitinib Inhibits the Chemotactic Activity of Monocytes via Proinflammatory Cytokine Production in Rheumatoid Arthritis Fibroblast-Like Synoviocytes. Cells. 2019 [6]Yang X, et al. Tofacitinib inhibits ox-LDL-induced adhesion of THP-1 monocytes to endothelial cells. Artif Cells Nanomed Biotechnol. 2019 Disclosure of Interests Cristina Garufi Consultant of: Lilly, Gloria Tucci: None declared, Ilenia Pacella: None declared, Marta Zagaglioni: None declared, Alessandra Pinzon Grimaldos: None declared, Fulvia Ceccarelli: None declared, Silvia Piconese: None declared, Francesca Romana Spinelli Consultant of: Lilly, Fabrizio Conti Consultant of: Lilly